8,749 research outputs found
Gamma-ray emission associated with Cluster-scale AGN Outbursts
Recent observations have revealed the existence of enormously energetic
~10^61 erg AGN outbursts in three relatively distant galaxy clusters. These
outbursts have produced bubbles in the intra-cluster medium, apparently
supported by pressure from relativistic particles and/or magnetic fields. Here
we argue that if > GeV particles are responsible then these particles are very
likely protons and nuclei, rather than electrons, and that the gamma-ray
emission from these objects, arising from the interactions of these hadrons in
the intra-cluster medium, may be marginally detectable with instruments such as
GLAST and HESS.Comment: 8 pages, 4 figures, accepted by MNRA
The general form of supersymmetric solutions of N=(1,0) U(1) and SU(2) gauged supergravities in six dimensions
We obtain necessary and sufficient conditions for a supersymmetric field
configuration in the N=(1,0) U(1) or SU(2) gauged supergravities in six
dimensions, and impose the field equations on this general ansatz. It is found
that any supersymmetric solution is associated to an structure. The structure is characterized by a null Killing
vector which induces a natural 2+4 split of the six dimensional spacetime. A
suitable combination of the field equations implies that the scalar curvature
of the four dimensional Riemannian part, referred to as the base, obeys a
second order differential equation. Bosonic fluxes introduce torsion terms that
deform the structure away from a covariantly
constant one. The most general structure can be classified in terms of its
intrinsic torsion. For a large class of solutions the gauge field strengths
admit a simple geometrical interpretation: in the U(1) theory the base is
K\"{a}hler, and the gauge field strength is the Ricci form; in the SU(2)
theory, the gauge field strengths are identified with the curvatures of the
left hand spin bundle of the base. We employ our general ansatz to construct
new supersymmetric solutions; we show that the U(1) theory admits a symmetric
Cahen-Wallach solution together with a compactifying pp-wave. The
SU(2) theory admits a black string, whose near horizon limit is . We also obtain the Yang-Mills analogue of the Salam-Sezgin solution of
the U(1) theory, namely , where the is supported by a
sphaleron. Finally we obtain the additional constraints implied by enhanced
supersymmetry, and discuss Penrose limits in the theories.Comment: 1+29 pages, late
A Description of Stroke Dynamics in 100 Meter Wheelchair Racing
Since wheelchair racing was introduced in the United States over thirty years ago, wheelchair sports have been experiencing a growing popularity.
An ever increasing number of national, and international competitions are being held for the disabled athlete; and record times in racing events are being set on an almost routine basis. Much interest by coaches, athletes, and researchers exists in identifying optimal performance factors in wheelchair propulsion, Three major areas of interest relating to performance have been the topics of recent research, symposia, and conferenees. These include the following: (1) designing effective training programs; (2) improving chair design; and (3) optimizing technique.
Elite disabled athletes are being profiled by researchers from both physiological and biomechanical perspectives. All wheelchair users stand to benefit from wheelchair sports and research. Where many everyday chair users once were in a heavy, awkward «hospital-type» chair that fitted no one and certainly wasn't designed for sports use, now light weight, easily maneuverable chairs are in use. As equipment is improved and propulsion techniques become more efficient, all chair users can benefit from such knowledge.
The United States Olympic Committee sponsored their first Sports Medieine and Sports Science Conference for the Disabled Athlete in the United States in March of 1987. This conference provided the opportunity for coaches, athletes, researchers, and other persons interested in sports for the disabled athlete to come together to share knowledge and ideas, and to examine the unique needs of the disabled performer. While physical limitations may influence the disabled athlete's perfomance, today's athletes are vitally interested in learning how to maximize their individual physical abilities.
Although the major thrust of a great many of the research studies investigating wheelchair athletes has often been of a physiologic nature, a growing body of biomechanic research on wheelchair propulsion has been identified (Ridgwaw, Pope & Wilkerson, 1987; Siler, Martin & Mungiole, 1987; Higgs, 1986; Sanderson & Sommer, 1985; Cerquiglini, Figura, Marchetti & Ricci, 1981; King, 1981; and Perry, 1981). Many of these investigations have included small sample sizes, have been limited to male subjects, and have included relatively few classes of wheelchair athletes. Additionally, few have studied the elite wheelchair athlete during commpetition.
The purpose of this study was to develop a kinematic model of wheelchair propulsion during 100-meter racing as performed by three classes of elite male wheelchair athletes
Semi-infinite cohomology of W-algebras
We generalize some of the standard homological techniques to \cW-algebras,
and compute the semi-infinite cohomology of the \cW_3 algebra on a variety of
modules. These computations provide physical states in \cW_3 gravity coupled
to \cW_3 minimal models and to two free scalar fields.Comment: 15 page
Adaptive Optical Phase Estimation Using Time-Symmetric Quantum Smoothing
Quantum parameter estimation has many applications, from gravitational wave
detection to quantum key distribution. We present the first experimental
demonstration of the time-symmetric technique of quantum smoothing. We consider
both adaptive and non-adaptive quantum smoothing, and show that both are better
than their well-known time-asymmetric counterparts (quantum filtering). For the
problem of estimating a stochastically varying phase shift on a coherent beam,
our theory predicts that adaptive quantum smoothing (the best scheme) gives an
estimate with a mean-square error up to times smaller than that
from non-adaptive quantum filtering (the standard quantum limit). The
experimentally measured improvement is
Gyromagnetic Ratio of Charged Kerr-Anti-de Sitter Black Holes
We examine the gyromagnetic ratios of rotating and charged AdS black holes in
four and higher spacetime dimensions. We compute the gyromagnetic ratio for
Kerr-AdS black holes with an arbitrary electric charge in four dimensions and
show that it corresponds to g=2 irrespective of the AdS nature of the
spacetime. We also compute the gyromagnetic ratio for Kerr-AdS black holes with
a single angular momentum and with a test electric charge in all higher
dimensions. The gyromagnetic ratio crucially depends on the dimensionless ratio
of the rotation parameter to the curvature radius of the AdS background. At the
critical limit, when the boundary Einstein universe is rotating at the speed of
light, it exhibits a striking feature leading to g=2 regardless of the
spacetime dimension. Next, we extend our consideration to include the exact
metric for five-dimensional rotating charged black holes in minimal gauged
supergravity. We show that the value of the gyromagnetic ratio found in the
"test-charge" approach remains unchanged for these black holes.Comment: New section added; 6 pages, RevTe
Kaluza-Klein Dyons in String Theory
S-duality of hetertotic / type II string theory compactified on a six
dimensional torus requires the existence of Kaluza-Klein dyons, carrying
winding charge. We identify the zero modes of the Kaluza-Klein monopole
solution which are responsible for these dyonic excitations, and show that we
get the correct degeneracy of dyons as predicted by S-duality. The self-dual
harmonic two form on the Euclidean Taub-NUT space plays a crucial role in this
construction.Comment: LaTeX file, 7 pages, reference adde
A Complete Classification of Higher Derivative Gravity in 3D and Criticality in 4D
We study the condition that the theory is unitary and stable in
three-dimensional gravity with most general quadratic curvature,
Lorentz-Chern-Simons and cosmological terms. We provide the complete
classification of the unitary theories around flat Minkowski and (anti-)de
Sitter spacetimes. The analysis is performed by examining the quadratic
fluctuations around these classical vacua. We also discuss how to understand
critical condition for four-dimensional theories at the Lagrangian level.Comment: 20 pages, v2: minor corrections, refs. added, v3: logic modified, v4:
typos correcte
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